Pipe wall thickness: Pipe wall thickness calculations as per ASME B31.3?

Pipe wall thickness


ASME B31.3 is used extensively for offshore facilities.
Pipe thickness under internal pressure calculated using equation given by this standard. ASME B31.8 normally used for gas lines in onshore production facilities and when transporting and distributing gas. ASME B31.4 normally used in onshore oil production and is actually subset of ASME B31.8 when it comes to calculating wall thickness. Therefore when it comes to calculating wall thickness, only ASME B31.3 and ASME B31.8 are in common use. In general ASME B31.8 is the more severe in calculating required wall thickness.



ASME B31.3

The wall thickness specified by ASME B31.3 for a given pipe can be calculated by:


tm  =  t + c                     


c  = the sum of mechanical allowance plus corrosion and erosion allowance
t   = pressure design thickness
tm = Minimum required thickness, including mechanical, corrosion, erosion allowance.


Where:-
                       
               
T=PD/2(SE+YP)
        t = required wall thickness
        E = Quality factor (table A-1A or A-1B)
        P = internal pipe pressure
        D = Pipe Outside Diameter
        S=Allowable Stress for pipe material (table A1)
        Y = coefficient (table 304.1.1)


Definition

Design Pressure – The maximum allowable working pressure at the design temperature or the most severe condition, which results in the greatest required component thickness and the highest component rating.

Design Temperature – the temperature at which, under the coincident pressure, the greatest thickness or higher component rating is required.

Design Minimum Temperature – The lowest component temperature expected in service.



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